Several patents and publications are cited in this description in order to more fully describe the state of the art to which this invention pertains. The entire disclosure of each of these patents and publications is incorporated by reference herein.
A variety of polymeric materials are used in structural and laminating applications that require optical clarity. For example, polymeric films or sheets made of acrylic polymers, polycarbonates, and polyesters are increasingly being used in glazing applications. While these clear plastic substrates may perform their structural function for extended periods of time, they are subject to surface scratching which can in turn mar their appearance and optical clarity. Accordingly, abrasion resistant hardcoats are often applied to protect the substrates.
One type of abrasion resistant hardcoat is derived from a polysiloxane coating composition made by hydrolyzing a tri-functional silane (e.g., methyltrimethoxysilane) in a mildly acidified colloidal silica solution (see e.g., U.S. Pat. Nos. 3,986,997; 4,027,073; 4,177,315; 4,355,135; 5,069,942 and European Pat. No. EP0157030). Past studies found that this type of polysiloxane based hardcoat adheres only moderately well to some substrates, in particular poly(ethylene terephthalate) (PET) films. Therefore, to improve adhesion, the poly(ethylene terephthalate) substrate films may be treated to enhance adhesion before the hardcoat is applied. One type of adhesion enhancement is to apply a layer of poly(alkyl amines), such as those described in U.S. Pat. Nos. 5,411,845; 5,770,312; 5,690,994; 5,698,329; and 7,189,457. Under high temperature and high humidity conditions, however, some polysiloxane hardcoats fail to maintain adequate adhesion to the poly(alkyl amine) primed substrates. There is still a need to further improve the polysiloxane coating composition to enhance the adhesion between the hardcoat and the poly(alkyl amine) primed substrates under various conditions.